Halogenobiphenyl derivatives

ABSTRACT

Halogenobiphenyl derivatives of Formula I ##STR1## wherein R 1  and R 2  are each alkyl or alkoxy in each case of 1-10 C atoms, Cy is 1,4-cyclohexylene, Ph is 1,4-phenylene, Q is --O--Cy-- or --O--Ph--, m and n are each 0 or 1 and X is F, Cl or Br, can be used as components of liquid crystal dielectrics for electrooptical display elements.

The present invention relates to new halogenobiphenyl derivatives havingliquid crystalline properties.

SUMMARY OF THE INVENTION

It is an object of this invention to provide new liquid crystalcompounds which are suitable as components of liquid crystaldielectrics, in particular for nematic phases with a high opticalanisotropy.

Upon further study of the specification and appended claims, furtherobjects and advantages of this invention will become apparent to thoseskilled in the art.

These objects have been achieved by providing halogenobiphenyl compoundsof Formula I ##STR2## wherein R¹ and R¹ are each alkyl or alkoxy each of1-10 C atoms, Cy is 1,4-cyclohexylene, Ph is 1,4-phenylene, Q is--O--Cy-- or --O--Ph--, m and n are each 0 or 1 and X is F, Cl or Br.

This invention also relates to the use of the compounds of Formula I ascomponents of liquid crystal dielectrics, liquid crystal dielectricscontaining at least one compound of Formula I, and electroopticaldisplay elements which contain such dielectrics.

DETAILED DISCUSSION

Like similar compounds, for example those known from GermanOffenlegungsschrift No. 2,800,553, these substances can be used ascomponent of liquid crystal dielectrics, in particular for displayswhich are based on the principle of the twisted cell.

It has been found that the compounds of Formula I are outstandinglysuitable as components of liquid crystal dielectrics. In particular,liquid crystal phases with a wide nematic range, a relatively highoptical anisotropy and a positive dielectric anisotropy can be preparedusing these compounds.

The compounds of Formula I are colorless in the pure state, and formliquid crystal mesophases in a temperature range which is advantageousfor electrooptical use.

Those compounds of Formula I which are optically active are suitable aschiral doping substances for the production of cholesteric phases suchas can also be used for White-Taylor dyestuff cells. In lowconcentrations, these chiral compounds are capable of preventinginterference with the optical phenomena in the twisted cell by "reversetwist" (compare Mol. Cryst. Liq. Cryst., Volume 34 (Letters), pages211-217 [1977]).

This invention thus relates to compounds of Formula I, and to a processfor their preparation, comprising diazotizing an aminobiphenylderivative of the Formula II ##STR3## wherein R¹, R², Cy, Ph, Q, m and nare as defined for Formula I, and replacing the diazonium group by an Xatom by known methods; or, for the preparation of a compound of FormulaI wherein R² is alkyl and n is 0, reacting a halogenobiphenyl derivativeof Formula III ##STR4## wherein R¹, Cy, Ph, m and X are as defined forFormula I, with a carboxylic acid of Formula IV

    HOOC--R.sup.3                                              IV

wherein R³ is alkyl of 1-10 C atoms, or with one of its reactivederivatives, in the presence of an acid or a Lewis acid; or for thepreparation of a compound of the Formula I wherein R² is alkoxy and/or nis 1, reacting a carboxylic acid of Formula V ##STR5## wherein R¹, Cy,Ph, m and X are as defined for Formula I, or one of its reactivederivatives, with a hydroxy compound of Formula IV

    H--(Q).sub.n --R.sup.4                                     VI

wherein R⁴ is alkoxy of 1-10 C atoms, or, when n is 1, also alkyl of1-10 C atoms, and Q and n are as defined for Formula I, or one of itsreactive derivatives.

In the preceding and following text, R¹, R², Cy, Ph, Q, m, n, X, R³ andR⁴ have the meaning given, unless expressly indicated otherwise.

The compounds of Formula I include ketones of Formula Ia and esters ofFormula Ib:

    R.sup.1 --(Cy).sub.m --Phx--Ph--CO--R.sup.3                Ia

    R.sup.1 --(Cy).sub.m --Phx--Ph--CO--(Q).sub.n --R.sup.4    Ib

wherein Phx is 1,4-phenylene radical substituted by an X atom.

Specifically, Formula I includes ketones of Formulae Ic and Id andesters of Formulae Ie to Ij:

    R.sup.1 --Phx--Ph--CO--R.sup.3                             Ic

    R.sup.1 --Cy--Phx--Ph--CO--R.sup.3                         Id

    R.sup.1 --Phx--Ph--COOR.sup.3                              Ie

    R.sup.1 --Phx--Ph--CO--O--Cy--R.sup.2                      If

    R.sup.1 --Phx--Ph--CO--O--Ph--R.sup.2                      Ig

    R.sup.1 --Cy--Phx--Ph--COOR.sup.3                          Ih

    R.sup.1 --Cy--Phx--Ph--CO--O--Cy--R.sup.2                  Ii

    R.sup.1 --Cy--Phx--Ph--CO--O--Ph--R.sup.2                  Ij

wherein the alkyl and alkoxy groups in each case contain 1-10,preferably 1-6 and in particular 3, 4, 5 or 6 C atoms.

The compounds of Formulae Id and Ie are preferred.

The radicals R¹ and R² are preferably alkyl.

In the compounds of Formulae I and Ia, Ib, Id, If, Ih, Ii and Ij, thosestereoisomers wherein the two substituents on the cyclohexylene radicalsare in each case in the trans-position relative to one another arepreferred.

In the compounds of Formulae I and Ia to Ij, the alkyl and alkoxy groupsare preferably straight-chained. Alkyl is preferably methyl, ethyl,n-propyl, n-butyl, n-pentyl or n-hexyl, and furthermore preferablyn-heptyl, n-octyl, n-nonyl or n-decyl; and alkoxy is preferably methoxy,ethoxy, n-propoxy, n-butoxy, n-pentyloxy or n-hexyloxy, and furthermorepreferably n-heptyloxy, n-octyloxy, n-nonyloxy or n-decyloxy.

Compounds of Formula I and Ia to Ij with branched alkyl or alkoxy groupsmay occasionally be of importance because of their better solubility inthe customary liquid crystal base materials, but especially as chiraldoping substances, if they are optically active. Branched groups of thistype as a rule contain not more than one chain branching. Preferredbranched alkyl radicals are isopropyl, 2-butyl (=1-methylpropyl),isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl (=3-methylbutyl),2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-heptyl (=1-methylhexyl),or 2-octyl (=1-methylheptyl); and preferred branched alkoxy radicals areisopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy,2-methylpentyloxy, 3-methylpentyloxy, 2-ethylhexyloxy, 1-methylhexyloxyand 1-methylheptyloxy.

The compounds of Formula I are otherwise prepared by methods which areknown per se, such as are described in the literature (for example inthe standard works, such as Houben-Weyl, Methoden der Organischen Chemie[Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), and inparticular under reaction conditions which are known and suitable forthe reactions mentioned. It is also possible to utilize variants whichare known per se and are not mentioned here in more detail.

If desired, the starting substances can also be formed in situ, in amanner such that they are not isolated from the reaction mixture but areimmediately reacted further to give the compounds of Formula I.

The halogenobiphenyl derivatives of Formula I can be prepared from theamines of Formula II by the methods of the Schiemann reaction (compare,for example, The Merck Index, 9th Edition, Merck & Co., Inc., Rahway,N.J., U.S.A., 1976, page ONR-80) or the Sandmeyer reaction (compare, forexample, The Merck Index, Loc.cit., page ONR-79).

Advantageously, the diazotization is first carried out with a salt orester of nitrous acid (such as NaNO₂ or butyl nitrite) in an aqueousacidic phase, it being possible to use as the acid, for example, HF,HCl, HBr, H₂ SO₄ or HBF₄, at temperatures of about -20° to +10°. Anadditional inert solvent may be present, for example an ether, such astetrahydrofuran or dioxane, or a hydrocarbon, such as toluene or xylene.

To prepare the chlorine compounds (I, X is F), the diazotization isadvantageously carried out in HBF₄. The diazonium tetrafluoborates arethereby formed, and can be decomposed at temperatures of only about 10°to 100°. If the diazotization is carried out with NaNO₂ in anhydrous HF,the desired fluorine compound is obtained directly by subsequentwarming.

The diazonium group is preferably replaced by Cl or Br in aqueoussolution in the presence of Cu₂ Cl₂ or Cu₂ Br₂ at temperatures of 30° to100°.

The ketones of Formula Ia (=I, R² is alkyl, n is 0) can furthermore beobtained by acylation of the halogenobiphenyl derivatives of Formula IIIwith carboxylic acids of Formula IV or their reactive derivatives,advantageously in the presence of an acid catalyst and an inert solventat temperatures of about 0° to about 120°. Suitable derivatives of thecarboxylic acids of Formula IV are, above all, their anhydrides andhalides, for example the corresponding acid chlorides and acid bromides.Suitable catalysts include acids, such as HF, H₃ PO₄ or polyphosphoricacid, or, preferably, Lewis acids, such as AlCl₃, AlBr₃, SnCl₄, ZnCl₂,FeCl₃, SbCl₅ or BF₃ or its etherate, and examples of suitable solventsinclude CS₂, hydrocarbons, such as hexane, nitrobenzene ortetramethylenesulfone.

The esters of Formula Ib can also be obtained by esterification of thecarboxylic acids of Formula V with alcohols or phenols of Formula VI.

Particularly suitable reactive derivatives of these carboxylic acids arethe acid halides, above all the chlorides and bromides, and furthermorethe anhydrides, for example also mixed anhydrides of the formula R¹--(Cy)_(m) --Phx--Ph--CO--O--COCH₃, azides and esters, in particularalkyl esters of 1-4 C atoms in the alkyl group.

Suitable reactive derivatives of the alcohols or phenols of Formula VIinclude, in particular, the corresponding metal alcoholates orphenolates of the formula M--(Q)_(n) --R⁴, in which M is one equivalentof a metal, preferably an alkali metal, such as Na or K.

The esterification is advantageously carried out in the presence of aninert solvent. Particularly suitable solvents include ethers, such asdiethyl ether, di-n-butyl ether, tetrahydrofuran, dioxane or anisole,ketones, such as acetone, butanone or cyclohexanone, amides, such asdimethylformamide or phosphoric acid hexamethyltriamide, hydrocarbons,such as benzene, toluene or xylene, halogenohydrocarbons, such as carbontetrachloride or tetrachloroethylene, and sulfoxides, such asdimethylsulfoxide or sulfolane. Water-immiscible solvents mayadvantageously be used at the same time for azeotropic distillation ofthe water formed during the esterification. An excess of an organicbase, for example pyridine, quinoline or triethylamine, may occasionallyalso be used as a solvent for the esterification. The esterification canalso be carried out in the absence of a solvent, for example by simpleheating of the components in the presence of sodium acetate.

The reaction temperature is usually -50° to +250°, preferably -20° to+80°. At these temperatures, the esterification reaction has as a ruleended after 15 minutes to 48 hours.

Specifically, the reaction conditions for the esterification largelydepend on the nature of the starting substance used. Thus, a freecarboxylic acid of Formula V is as a rule reacted with an alcohol orphenol of Formula VI in the presence of a strong acid, for example amineral acid, such as hydrochloric acid or sulfuric acid.

A preferred procedure is the reaction of an acid anhydride or, inparticular, an acid chloride with an alcohol, preferably in a basicmedium, typical bases being alkali metal hydroxides, such as sodium orpotassium hydroxide, alkali metal carbonates or bicarbonates, such assodium carbonate, sodium bicarbonate, potassium carbonate or potassiumbicarbonate, alkali metal acetates, such as sodium or potassium acetate,alkaline earth metal hydroxides, such as calcium hydroxide, or organicbases, such as triethylamine, pyridine, lutidine, collidine orquinoline.

Another preferred embodiment of the process according to this inventioncomprises first converting the hydroxy compound of Formula VI to beesterified into the sodium alcoholate or phenolate or potassiumalcoholate or phenolate, for example by treatment with ethanolic sodiumhydroxide solution or potassium hydroxide solution, isolating thisalcoholate or phenolate, suspending it in acetone or diethyl ether,together with sodium bicarbonate or potassium carbonate, while stirring,and adding a solution of the acid chloride or anhydride in diethylether, acetone or dimethylformamide to this suspension, advantageouslyat temperatures of about -25° to +20°.

Some of the starting substances of Formulae II to VI and their reactivederivatives are known, and all of them can be prepared analogously bythe methods for known compounds, from substances which are known fromthe literature.

Thus, the amines of Formula II can be obtained, for example, bynitration of biphenyl derivatives (corresponding to Formula I, but X isH) and subsequent reduction, and the starting substances of Formulae IIIand V can be obtained analogously from the unsubstituted compounds(corresponding to Formulae III and V, but X is H), by nitration,reduction to give the amino compound, diazotization and a Schiemann orSandmeyer reaction.

The dielectrics according to this invention comprise 2 to 15, preferably3 to 12, components, at least one of which is a compound of Formula I.The other constituents are preferably selected from the nematic ornematogenic substances, in particular the known substances, from theclasses of azoxybenzenes, benzylideneanilines, biphenyls, terphenyls,phenyl- or cyclohexyl-benzoates, phenyl or cyclohexylcyclohexanecarboxylates, phenylcyclohexanes, cyclohexylbiphenyls,cyclohexylcyclohexanes, cyclohexylnaphthalenes,1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl- orcyclohexyl-pyrimidines, phenyl- or cyclohexyl-dioxanes, optionallyhalogenated stilbenes, benzyl phenyl ethers, tolanes and substitutedcinnamic acids. The most important compounds which can be used asconstituents of such liquid crystal dielectrics can be characterized byFormula VII

    R.sup.5 --A--G--E--R.sup.6                                 VII

wherein A and E are each a carbocyclic or heterocyclic ring system fromthe group comprising 1,4-disubstituted benzene and cyclohexane rings,4,4'-disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexanesystems, 2,5-disubstituted pyrimidine and 1,3-dioxane rings,2,6-disubstituted naphthalene, di- and tetra-hydronaphthalene,quinazoline and tetrahydroquinazoline; G is --CH═CH--, --CH═CL--,--CH.tbd.C--, --CO--O--, --CO--S--, --CH═N--, --N(O)═N--, --CH═N(O)--,CH₂ --CH₂ --, --CH₂ --O--, --CH₂ --S--, --COO--Ph--COO-- or a C--Csingle bond; L is halogen, preferably chlorine, or CN; and R⁵ and R⁶ arealkyl, alkoxy, alkanoyloxy or alkoxycarbonyloxy with up to 18,preferably up to 8, carbon atoms, or one of these radicals is also CN,NC, NO₂, CF₃, F, Cl or Br. In most of these compounds, R⁵ and R⁶ differ,one of these radicals usually being an alkyl or alkoxy group. Many suchsubstances or mixtures thereof are commercially available.

The dielectrics according to this invention contain about 0.1 to 30%,preferably 2 to 25%, of one or more compounds of Formula I.

The dielectrics according to this invention are prepared in a mannerwhich is customary per se. As a rule, the components are dissolved inone another, advantageously at elevated temperature. If a temperatureabove the clear point of the main constituent is chosen, thecompleteness of the solution operation can be particularly easilyobserved.

The liquid crystal dielectrics according to this invention can bemodified by suitable additives such that they can be used in all thetypes of liquid crystal display elements which have hitherto beendisclosed.

Such additives are familiar to the expert and are described in detail inthe literature. For example, dichroic dyestuffs or substances formodifying the dielectric anisotropy, the viscosity, the conductivityand/or the orientation of the nematic phases can be added. Suchsubstances are described, for example, in German OffenlegungsschriftenNos. 2,209,127, 2,240,864, 2,321,632, 2,338,281, 2,450,088, 2,637,430,2,853,728 and 2,902,177.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description utilize the present invention toits fullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever. In the followingexamples and in the preceding text, all temperatures are set forthuncorrected in degrees Celsius and all parts and percentages are byweight, unless otherwise indicated.

In the examples, m.p. is the melting point and c.p. is the clear pointof a liquid crystal substance.

EXAMPLE 1

180 ml of 35% aqueous tetrafluoboric acid solution is added dropwise toa suspension of 36.7 g of4'-acetyl-2-amino-4-(trans-4-pentylcyclohexyl)-biphenyl (m.p. 118°-123°;obtainable by nitration of4'-acetyl-4-(trans-4-pentylcyclohexyl)-biphenyl and subsequenthydrogenation of the resulting crude 2-nitro compound over Raney nickelin tetrahydrofuran) in 180 ml of dioxane at 15°-20°, while stirring, anda solution of 7.2 g of NaNO₂ in 25 ml of water is then added dropwise at0°. The mixture is subsequently stirred for 6 hours, the temperaturebeing allowed to rise to 15°. After customary working up (extractionwith toluene, filtration over silica gel),4'-acetyl-2-fluoro-4-(trans-4-pentylcyclohexyl)-biphenyl of m.p. 81° andc.p. 170° is obtained.

EXAMPLES 2 TO 49

The following compounds are obtained analogously to Example 1 from thecorresponding amino compounds:

2. 4'-Acetyl-2-fluoro-4-methylbiphenyl.

3. 4'-Acetyl-2-fluoro-4-ethylbiphenyl.

4. 4'-Acetyl-2-fluoro-4-propylbiphenyl.

5. 4'-Acetyl-2-fluoro-4-butylbiphenyl.

6. 4'-Acetyl-2-fluoro-4-pentylbiphenyl.

7. 4'-Acetyl-2-fluoro-4-hexylbiphenyl.

8. 4'-Acetyl-2-fluoro-4-heptylbiphenyl.

9. 4'-Acetyl-2-fluoro-4-octylbiphenyl.

10. 4'-Acetyl-2-fluoro-4-nonylbiphenyl.

11. 4'-Acetyl-2-fluoro-4-decylbiphenyl.

12. 4'-Acetyl-2-fluoro-4-methoxybiphenyl.

13. 4'-Acetyl-2-fluoro-4-ethoxybiphenyl.

14. 4'-Acetyl-2-fluoro-4-propoxybiphenyl.

15. 4'-Acetyl-2-fluoro-4-butoxybiphenyl.

16. 4'-Acetyl-2-fluoro-4-pentyloxybiphenyl.

17. 4'-Acetyl-2-fluoro-4-hexyloxybiphenyl.

18. 4'-Acetyl-2-fluoro-4-heptyloxybiphenyl.

19. 4'-Acetyl-2-fluoro-4-octyloxybiphenyl.

20. 4'-Acetyl-2-fluoro-4-nonyloxybiphenyl.

21. 4'-Acetyl-2-fluoro-4-decyloxybiphenyl.

22. 4'-Acetyl-2-fluoro-4-(trans-4-methylcyclohexyl)-biphenyl.

23. 4'-Acetyl-2-fluoro-4-(trans-4-ethylcyclohexyl)-biphenyl.

24. 4'-Acetyl-2-fluoro-4-(trans-4-propylcyclohexyl)-biphenyl.

25. 4'-Acetyl-2-fluoro-4-(trans-4-butylcyclohexyl)-biphenyl.

26. 4'-Acetyl-2-fluoro-4-(trans-4-hexylcyclohexyl)-biphenyl.

27. 4'-Acetyl-2-fluoro-4-(trans-4-heptylcyclohexyl)-biphenyl.

28. 4'-Acetyl-2-fluoro-4-(trans-4-octylcyclohexyl)-biphenyl.

29. 4'-Acetyl-2-fluoro-4-(trans-4-nonylcyclohexyl)-biphenyl.

30. 4'-Acetyl-2-fluoro-4-(trans-4-decylcyclohexyl)-biphenyl.

31. 4'-Acetyl-2-fluoro-4-(trans-4-methoxycyclohexyl)-biphenyl.

32. 4'-Acetyl-2-fluoro-4-(trans-4-ethoxycyclohexyl)-biphenyl.

33. 4'-Acetyl-2-fluoro-4-(trans-4-propoxycyclohexyl)-biphenyl.

34. 4'-Acetyl-2-fluoro-4-(trans-4-butoxycyclohexyl)-biphenyl.

35. 4'-Acetyl-2-fluoro-4-(trans-4-pentyloxycyclohexyl)-biphenyl.

36. 4'-Acetyl-2-fluoro-4-(trans-4-hexyloxycyclohexyl)-biphenyl.

37. 4'-Acetyl-2-fluoro-4-(trans-4-heptyloxycyclohexyl)-biphenyl.

38. 4'-Acetyl-2-fluoro-4-(trans-4-octyloxycyclohexyl)-biphenyl.

39. 4'-Acetyl-2-fluoro-4-(trans-4-nonyloxycyclohexyl)-biphenyl.

40. 4'-Acetyl-2-fluoro-4-(trans-4-decyloxycyclohexyl)-biphenyl.

41. 2-Fluoro-4'-propionyl-4-propylbiphenyl.

42. 2-Fluoro-4'-propionyl-4-butylbiphenyl.

43. 2-Fluoro-4'-propionyl-4-pentylbiphenyl.

44. 2-Fluoro-4'-propionyl-4-methoxybiphenyl.

45. 2-Fluoro-4'-propionyl-(trans-4-propylcyclohexyl)-biphenyl.

46. 2-Fluoro-4'-propionyl-(trans-4-pentylcyclohexyl)-biphenyl.

47. 4'-Butyryl-2-fluoro-4-(trans-4-propylcyclohexyl)-biphenyl.

48. 4'-Decanoyl-2-fluoro-4-(trans-4-pentylcyclohexyl)-biphenyl.

49. 4'-Acetyl-3-fluoro-4-(trans-4-pentylcyclohexyl)-biphenyl.

EXAMPLE 50

A solution of 7.2 g of NaNO₂ in 25 ml of water is added to a suspensionof 36.7 g of 4'-acetyl-2-amino-4-(trans-4-pentylcyclohexyl)-biphenyl in150 ml of 15% aqueous hydrochloric acid at -5° in the course of 0.5hours. The solution thus obtained is added dropwise, at 0°-5° in thecourse of 1 hour, to a Cu(I) salt solution which has been prepared from25 g of CuSO₄.5H₂ O, 8.8 g of NaCl, 6.3 g of Na₂ SO₃, 100 ml of waterand 40 ml of 32% hydrochloric acid. After the mixture has been heated to40° for half an hour, it is cooled and extracted with CH₂ Cl₂ and theproduct is worked up in the customary manner.4'-Acetyl-2-chloro-4-(trans-4-pentylcyclohexyl)-biphenyl is obtained.

EXAMPLES 51 TO 55

The following compounds are obtained analogously to Example 50 from thecorresponding amino compounds:

51. 2-Chloro-4'-acetyl-4-propylbiphenyl.

52. 2-Chloro-4'-acetyl-4-butylbiphenyl.

53. 2-Chloro-4'-acetyl-4-pentylbiphenyl.

54. 2-Chloro-4'-acetyl-4-(trans-4-propylcyclohexyl)-biphenyl.

55. 2-Chloro-4'-acetyl-4-(trans-4-pentylcyclohexyl)-biphenyl.

EXAMPLE 56

The procedure followed is analogous to Example 50, but HBr is usedinstead of HCl and NaBr is used instead of NaCl, and4'-acetyl-2-bromo-4-(trans-5-pentylcyclohexyl)-biphenyl is obtained.

EXAMPLE 57

27 g of AlCl₃ is added to a mixture of 32.4 g of2-fluoro-4-(trans-4-pentylcyclohexyl)-biphenyl and 200 ml of CS₂ at 20°,while stirring; 10 g of acetic anhydride is then added dropwise, whilestirring and boiling, and the mixture is boiled for another hour. Themixture is cooled, filtered and decomposed by being discharged intohydrochloric acid/ice, and4'-acetyl-2-fluoro-4-(trans-4-pentylcyclohexyl)-biphenyl of m.p. 81° andc.p. 170° is obtained.

The compounds mentioned in Examples 2 to 56 can be obtained analogously.

EXAMPLE 58

28.6 g of 2'-fluoro-4'-pentylbiphenyl-4-carboxylic acid (obtainable bynitration of 4'-pentylbiphenyl-4-carboxylic acid to give the 2'-nitroderivative, reduction to give the 2'-amino compound and a Schiemannreaction) is boiled with 24 g of SOCl₂ for one hour, the mixture isevaporated, the resulting crude acid chloride is dissolved in 150 ml oftoluene, 7.9 g of pyridine and 6 g of propanol are added and the mixtureis boiled for 2 hours. The mixture is cooled and washed with water andthe organic phase is dried over Na₂ SO₄ and evaporated. Propyl2'-fluoro-4'-pentylbiphenyl-4-carboxylate is obtained. Analogously,there are obtained:

59. Methyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

60. Ethyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

61. Propyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

62. Butyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

63. Pentyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

64. Hexyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

65. Heptyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

66. Octyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

67. 1-Methylheptyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

68. Nonyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

69. Decyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

70. Trans-4-propylcyclohexyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

71. Trans-4-butylcyclohexyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

72. Trans-4-pentylcyclohexyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

73. p-Propylphenyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

74. p-Butylphenyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

75. p-Pentylphenyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

76. p-Methoxyphenyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

77. p-Ethoxyphenyl 2'-fluoro-4'-propylbiphenyl-4-carboxylate.

78. Ethyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

79. Propyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

80. Butyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

81. Pentyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

82. Hexyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

83. 1-Methylheptyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

84. Trans-4-propylcyclohexyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

85. Trans-4-pentylcyclohexyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

86. p-Propylphenyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

87. p-Pentylphenyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

88. p-Methoxyphenyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

89. p-Ethoxyphenyl 4'-butyl-2'-fluorobiphenyl-4-carboxylate.

90. Ethyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

91. Butyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

92. Pentyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

93. Hexyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

94. 1-Methylheptyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

95. Trans-4-propylcyclohexyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

96. Trans-4-pentylcyclohexyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

97. p-Propylphenyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

98. p-Pentylphenyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

99. p-Methoxyphenyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

100. p-Ethoxyphenyl 2'-fluoro-4'-pentylbiphenyl-4-carboxylate.

101. Ethyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

102. Propyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

103. Butyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

104. Pentyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

105. Hexyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

106. 1-Methylheptyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

107. Trans-4-propylcyclohexyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

108. Trans-4-pentylcyclohexyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

109. p-Propylphenyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

110. p-Pentylphenyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

111. p-Methoxyphenyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

112. p-Ethoxyphenyl2'-fluoro-4'-(trans-4-propylcyclohexyl)-biphenyl-4-carboxylate.

113. Ethyl 4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

114. Propyl4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

115. Butyl 4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

116. Pentyl4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

117. Hexyl 4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

118. 1-Methylheptyl4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

119. Trans-4-propylcyclohexyl4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

120. Trans-4-pentylcyclohexyl4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

121. p-Propylphenyl4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

122. p-Pentylphenyl4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

123. p-Methoxyphenyl4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

124. p-Ethoxyphenyl4'-(trans-4-butylcyclohexyl)-2'-fluorobiphenyl-4-carboxylate.

125. Ethyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate, m.p.53.5°, c.p. 153.4°.

126. Propyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate.

127. Butyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate, m.p.52°, c.p. 120.3°.

128. Pentyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate.

129. Hexyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate.

130. 1-Methylheptyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate.

131. Trans-4-propylcyclohexyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate.

132. Trans-4-pentylcyclohexyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate.

133. p-Propylphenyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate.

134. p-Pentylphenyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate.

135. p-Methoxyphenyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate.

136. p-Ethoxyphenyl2'-fluoro-4'-(trans-4-pentylcyclohexyl)-biphenyl-4-carboxylate.

Examples of dielectrics containing at least one compound of Formula Ifollow:

EXAMPLE A

A mixture of 28% of p-(trans-4-pentylcyclohexyl)-benzonitrile, 11% of2-p-cyanophenyl-5-pentyl-1,3-dioxane, 32% of 4-pentyl-4'-cyanobiphenyl,9% of 4-(trans-4-pentylcyclohexyl)-4'-cyanobiphenyl and 20% of4'-acetyl-2-fluoro-4-(trans-4-pentylcyclohexyl)-biphenyl has a m.p. of-11° and a c.p. of 80°.

EXAMPLE B

A mixture of 18% of p-(trans-4-propylcyclohexyl)-benzonitrile, 26% ofp-(trans-4-pentylcyclohexyl)-benzonitrile, 13% p-ethoxyphenyltrans-4-propylcyclohexanecarboxylate, 12% of p-ethoxyphenyltrans-4-butylcyclohexanecarboxylate, 14% of p-methoxyphenyltrans-4-pentylcyclohexanecarboxylate and 17% of4'-acetyl-2-fluoro-4-(trans-4-pentylcyclohexyl)-biphenyl has a m.p. of-14° and a c.p. of 77°.

EXAMPLE C

A mixture of 13% of p-(trans-4-ethylcyclohexyl)-benzonitrile, 18% ofp-(trans-4-propylcyclohexyl)-benzonitrile, 13% ofp-(trans-4-butylcyclohexyl)-benzonitrile, 25% ofp-(trans-4-pentylcyclohexyl)-benzonitrile, 15% ofp-(trans-4-heptylcyclohexyl)-benzonitrile and 16% of4'-acetyl-2-fluoro-4-(trans-4-pentylcyclohexyl)-biphenyl has a m.p. of-17° and a c.p. of 58°.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples. From the foregoing description, one skilled in the art caneasily ascertain the essential characteristics of this invention, andwithout departing from the spirit and scope thereof, can make variouschanges and modifications of the invention to adapt it to various usagesand conditions.

What is claimed is:
 1. A liquid crystal dielectric useful inelectrooptical display elements, comprising at least two liquid crystalcomponents, at least one component being an halogenobiphenyl compound ofthe formula ##STR6## wherein R¹ and R² are each alkyl or alkoxy each of1-10 C atoms; Cy is 1,4-cyclohexylene; Ph is 1,4-phenylene; Q is--O--Cy-- or --O--Ph; m and n are each 0 or 1; and X is F, Cl or Br,with the proviso that when R¹ and R² are both alkoxy, and m and n areboth 0, then X is not F or Cl.
 2. A dielectric of claim 1 comprising2-15 liquid crystalline components.
 3. A dielectric of claim 1 whereinthe amount of said halogenobiphenyl compound is 0.1-30%.
 4. A dielectricof claim 1 wherein, in said halogenobiphenyl compound, R¹ and R² arestraight chained.
 5. A dielectric of claim 1 wherein saidhalogenobiphenyl compound is of the formula

    R.sup.1 --Cy--Phx--Ph--CO--R.sup.3

    R.sup.1 --Phx--Ph--COOR.sup.3

wherein R³ is C₁₋₁₀ -alkyl and Phx is 1,4-phenylene substituted by X. 6.A dielectric of claim 1 wherein said halogenobiphenyl compound is of theformula

    R.sup.1 --Phx--Ph--CO--R.sup.3

    R.sup.1 --Phx--Ph--CO--O--Cy--R.sup.2

    R.sup.1 --Phx--Ph--CO--O--Ph--R.sup.2

    R.sup.1 --Cy--Phx--Ph--COOR.sup.3

    R.sup.1 --Cy--Phx--Ph--CO--O--Cy--R.sup.2

    R.sup.1 --Cy--Phx--Ph--CO--O--Ph--R.sup.2

wherein R³ is C₁₋₁₀ -alkyl and Phx is 1,4-phenylene substituted by X. 7.In an electrooptical display element comprising a liquid crystal cell,the improvement wherein the liquid crystal cell comprises a dielectricof claim
 1. 8. A dielectric of claim 1 wherein X is in the 2'-positionwith respect to the adjacent unsubstituted 1,4-phenylene group.
 9. Adielectric of claim 1 wherein one or both of m and n are
 1. 10. Adielectric of claim 1 wherein m=n=0 and R¹ is alkyl.
 11. A dielectric ofclaim 1 wherein m=n=0 and X is Br.